Reuters Image caption Some 3.5 million passengers and 40,000 drivers use the Uber app in London
Hundreds of thousands of people have signed a petition calling for Transport for London to reverse its decision not to renew Uber's licence.
On Friday, the regulator said Uber was not "fit and proper" to hold a London private hire operator licence on the grounds of "public safety and security implications".
More than 400,000 names have since been added to Uber's petition on Change.org.
The ride-hailing app firm says it will appeal against TfL's decision.
The petition, started by Uber London, says:"If this decision stands, it will put more than 40,000 licensed drivers out of work and deprive millions of Londoners of a convenient and affordable form of transport."
TfL's concerns include Uber's approach to carrying out background checks on drivers and reporting serious criminal offences.
Uber's licence is due to expire on 30 September.
It has 21 days to appeal against TfL's decision and can continue to operate while any appeals are ongoing.
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Drivers and passengers react to news that Uber's licence in London will be revoked
Petitioner Glenn Gathercole, from London, said he added his signature because:"Uber provides a much needed alternative to minicabs and black cabs.It is more efficient, safer and economical than the alternatives."
And Twitter user @Gabbysalaza_ said that she was "annoyed" at the decision as Uber allowed her to get out of "uncomfy" situations if out at night.
Others have said that the ruling was within the company's control.
"Uber knew the rules.TFL asked them to comply with the rules.Uber refused.What is TFL supposed to do?" said political commentator Owen Jones.
Danielle Louise wrote on Twitter:"Londoners are literally more outraged at the loss of Uber than the fact women are being sexually assaulted in fake taxis."
'London is closed'
Mayor of London Sadiq Khan has given his full support to TfL's decision.
"It would be wrong if TfL continued to license Uber if there is any way that this could pose a threat to Londoners' safety and security," he said.
But Conservative MP and minister for London Greg Hands said, while the company must address safety concerns, Mr Khan was threatening to leave users "stranded" and put thousands out of work.
Uber has said the move "would show the world that, far from being open, London is closed to innovative companies".
Some 3.5 million passengers and 40,000 drivers use the Uber app in London....
- Chief executive Travis Kalanick, who helped found the company in 2009, resigned in July following a series of scandals and criticism of his management style
- In June, 20 staff were sacked after a law firm investigated specific complaints made to the company about sexual harassment, bullying, and retaliation for reporting problems
- At the start of 2017, the firm paid £16.2m ($20m) in the US to settle allegations it gave false promises to drivers over how much they would earn
- In October 2016 Uber lost a landmark employment tribunal in the UK that ruled drivers should be classed as workers rather than being self-employed
- A few months later Uber announced it would offer English courses, financial advice and introduce an appeals panel for its UK workers after facing criticism over lack of support and rights for its drivers
- In 2015 the New Delhi government banned app-based taxi companies after an Uber driver raped a passenger in his vehicle
- Uber stopped operating in Austin, Texas, when it was told drivers would have to have fingerprint background checks, but it reinstated its services after the requirement was ended
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